1. Field of the Invention
This invention relates generally to headphones, and more specifically, to enhancing the generation of three-dimensional sound in headphones.
2. Background Discussion
Human ears typically perceive two signals (i.e., one at each ear), whereby based on these signals, they are able extract enough information to determine the location from which sound emanated with respect to the three-dimensional space around them. Since the human hearing faculty is able to three-dimensionally discern sounds from the real world around us, it is therefore possible to create the same effect from two speakers or a set of headphones. The localization of sound based on hearing comes from a few mechanisms associated with human hearing. For example, Inter-aural Intensity Difference (IID) refers to the fact that a sound source appears louder at the ear that it is closest to, while Inter-aural Time Difference (ITD) refers to sound arriving earlier at the ear it is closest to. The combination of IID and ITD mechanisms provide a means for the primary localization of sound while the pinna, which is the outer structure of the ear, provides a filtering mechanism (i.e., outer ear effects) that allows the brain to accurately determine the location of the sound. As sound travels, it experiences different effects during propagation, such as, for example, reflection, diffraction, attenuation, etc. By hearing these effects, we are able to perceive certain information about the environment around us (e.g., room size, etc.).
In order to generate sound as it is heard in our three-dimensional surroundings, various listening cues such as IID, ITD, and outer ear effects may be recreated (i.e., electronically) by manipulating the audio reaching our ears. The advent of high performance digital signal processing hardware and tools has lent itself to the development of various digital filtering techniques used in the reproduction of headphone-based three-dimensional sound reproduction. For example, Head-Related Transfer Functions (HRTF) utilized within digital signal processors provide filtering means capable of creating the illusion of three-dimensional sound for the headphone-user.
Thus, it would be an advancement in the state of the art to enhance the three-dimensional effect of reproduced sound in audio headphone technology.